1. Field of the Invention
This invention relates to a compression regenerative machine for a fuel cell that is used for a fuel cell system.
2. Description of the Related Art
A compression regenerative machine for a fuel cell is connected to a fuel cell in a fuel cell system used for a car as described in, for example, Japanese Unexamined Patent Publication (Kokai) No. 7-14599. In fuel cells in general, a pair of separators is disposed on both sides of an electrolyte layer. Feed grooves for supplying a fuel and an oxygen-containing gas are formed in these separators. One of the separators supplies a hydrogen-containing fuel and the other separator supplies an oxygen-containing gas such as air. In consequence, electrons move due to the chemical reaction between hydrogen and oxygen to provide a current. A fuel feed pipe and an air feed pipe are connected to the upstream side of such a fuel cell to supply the fuel and air, respectively. The air feed pipe is open to the atmosphere through a compressor that is driven by a motor. The compressor pressurizes air from the atmosphere to a predetermined pressure and supplies the air to the fuel cell. An air exhaust pipe is connected to the downstream side of the fuel cell to exhaust an exhaust gas, after oxygen is extracted from air inside the fuel cell, to the atmosphere. A regenerator, which is connected to the air exhaust pipe, assists the motor operating the compressor by using its power that is generated as the exhaust gas is expanded in the regenerator. In the fuel cell device of this kind, each of the compressor and the regenerator employs a compressor and regenerator for a fuel cell separately. In this fuel cell system, the compressor and the regenerator are constituted so that they can be operated by the same driving source.
In the conventional fuel cell system, however, no examination has been made of the capacity ratio between a closed compression chamber defined by the compressor and a closed regenerative chamber defined by the regenerator. Therefore, high power generation performance of the fuel cell has not been maintained easily, and its production cost has increased.
The fuel cell generates current by the reaction between hydrogen in the fuel and oxygen in the oxygen-containing gas, as described above. If the difference between the pressure of the fuel and the pressure of the oxygen-containing gas becomes great depending on the capacity ratio of the compression chamber to the regeneration chamber, a large load acts on the electrolyte layer inside the fuel cell with possible breakage of the electrolyte layer. Therefore, the conventional fuel cell device involves the problem of durability.
To have the pressure of the fuel and the pressure of the oxygen-containing gas uniform within a suitable range in the fuel cell system, it may be possible, in principle, to adjust the pressure of either one of the fuel and the oxygen-containing gas so as to reduce the load acting on the electrolyte layer. However, when means for adjusting the pressure of the fuel is added, the means becomes large in scale because hydrogen is supplied generally by the chemical decomposition of the fuel such as a natural gas, methanol, or the like. Eventually, the cost of production of the fuel cell system becomes high. When the pressure of the oxygen-containing gas is adjusted, oxygen cannot be supplied into the fuel cell if its pressure drops remarkably. In either case, the fuel cell system cannot maintain a high power generation performance.
In view of the problems described above, it is an object of the present invention to provide a compression regenerative machine for a fuel cell that can exhibit high durability while maintaining a high power generation performance of the fuel cell system and can prevent an increase in the production cost.
According to one aspect of the present invention, there is provided a compression regenerative machine, for a fuel cell, that includes a compression mechanism portion of a displacement type, connected to an oxygen-containing gas supply side of a fuel cell and a regenerative mechanism portion of a displacement type, connected to an exhaust gas discharge side of the fuel cell, wherein a closed compression chamber defined by the compression mechanism portion and a closed regenerative chamber defined by the regenerative mechanism portion have a capacity ratio of 1.25 to 3.
This compression regenerative machine for a fuel cell comprises a compression mechanism portion for supplying an oxygen-containing gas to a fuel cell, connected to an oxygen-containing gas supply side of a fuel cell, and a regenerative mechanism portion for expanding an exhaust gas discharged from the fuel cell, connected to an exhaust gas discharge side of the fuel cell.
The inventors of the present invention have discovered through experiments a capacity ratio between the compression chamber and the regenerative chamber from a preferred range of the pressure of the oxygen-containing gas to be supplied to the fuel cell. According to such experiments, a capacity ratio of capacity A (cc) of the closed compression chamber defined by the compression mechanism portion and the capacity B (cc) of the closed regenerative chamber defined by the regenerative mechanism portion is
xe2x80x83(A/B)=1.25 to 3.
In the compression regenerative machine for a fuel cell according to the present invention, the capacity ratio between the compression chamber and the regenerative chamber falls within this range. Therefore, the difference between the pressure of the fuel and the pressure of the oxygen-containing gas becomes small, a large load does not act on the electrolyte layer inside the fuel cell, and damage of the electrolyte layer can be prevented. In this instance, the pressure of the oxygen-containing gas is not lowered markedly. Therefore, a sufficient amount of oxygen can be supplied to the fuel cell, and high power generation performance of the fuel cell system can be maintained.
The compression regenerative machine for a fuel cell according to the present invention regulates the pressure of the oxygen-containing gas but need not regulate the pressure of the fuel that would otherwise require a large-scale setup. Therefore, the production cost of the fuel cell device can be lowered.
The compression regenerative machine for a fuel cell according to the present invention can thus maintain a high durability while the fuel cell device maintains a high power generation performance, and can prevent an increase in the production cost.
The present invention may be more fully understood from the description of preferred embodiments of the invention set forth below, together with the accompanying drawings.